The present invention relates to micro-mechanical electrical systems (MEMS) type device for measuring vibration and movement, and more particularly to a MEMS accelerometer.
MEMS type devices for use as sensors and accelerometers are well known. Such devices are generally fabricated on a silicon or related planar substrate by semi-conductor manufacturing type methods, such as the use of photoresists, masks and various etching processes to fabricate a proximity sensor that includes a suspended proof mass member and means to measure the deflection of the proof mass suspending means. Such devices have inherent limitations on the minimum size, detection limit, sensitivity and the like, largely due to the means used for detecting the deflection of the proof mass.
In particular, as attempts have been made to miniaturize accelerometer devices for diverse applications using the technology prior to this applicants invention important aspects of performance have been compromised. In particular, it has been difficult for the prior art devices to achieve both a low noise floor and the required capacitive sensitivity.
Although accelerometers with a noise floor of less than 1 μg/√Hz have been reported they include a very large proof mass in the order of several square millimeters. In particular, there has been an unmet need for accelerometer devices with a size of less than about 1.5×1.5 mm, and more preferably less than about 1 mm×1 mm.
It is therefore a first object of the present invention to provide an accelerometer with a reduced minimum detection limit.
It is another object of the invention to provide an accelerometer with smaller physical dimensions than the prior art.
It is still a further object to provide an accelerometer having the above attributes with a higher sensitivity.
It is also an object of the invention to provide an accelerometer subject to lower mechanical noise.
A still further and additional object of the invention is to provide the aforementioned benefits in an accelerometer that can be fabricated using standard silicon on insulator (SOI) fabrication techniques generally known in he semiconductor industry to reduce manufacturing costs.
It is still a further object of the invention to provide a means to combine multiple accelerometers in a configuration for the simultaneous measurement acceleration in three dimensions.
It is still a further object of the invention to provide an accelerometer which doesn't require vacuum packaging in order to operate, thus enabling the benefits of lower packaging costs, smaller packaging size and stability of operation.